In recent years, polythiophene and its derivatives have received increasing attention as an important class of electrically conducting polymers for their potential commercial and military applications in advanced materials, for example, electroactive, optical, anti-corrosion, electromagnetic-shielding and biomedical materials, and in construction of new types of other electronic materials, for example, microelectrodes, batteries, sensors and electronic devices.
Polythiophene and its derivatives can be prepared by (i) chemical or (ii) electrochemical oxidation of thiophene and its derivatives as represented by the following equation: ##STR2## The published literature and patents describe a number of methods for preparing polythiophene.
The electrochemical polymerization of thiophene generally requires a high applied potential of at least about 1.6 volts (V) versus (vs.) saturated calomel electrode (SCE) in comparison with the relatively low applied potentials required for the preparation of polyaniline and polypyrrole (about 0.7 or 0.8 V vs. SCE). However, the polythiophene polymers so prepared decompose readily at high potentials, often resulting in substandard quality of the polymers. Moreover, the processes disclosed in the scientific literature and previous patents for electrochemically polymerizing thiophene generally provide reactions having slow reaction rates.
Chemical preparation of polythiophene and its derivatives is usually carried out via a polycondensation of 2,5-dihalothiophenes by dehalogenation with magnesium in the presence of transition metal catalysts. The chemical synthesis involves multi-step reactions and is generally economically inefficient and time-consuming. In addition, the polythiophenes prepared via chemical synthetic methods generally have lower conductivities, for example, about 10.sup.-2 to about 10 Siemens per centimeter (S/cm), as compared to polythiophenes prepared electrochemically (about 10.sup.2 S/cm).
In addition, most of the previous work in the field of polythiophenes has been devoted to the study of the physicochemical and electrical properties of the polymers and to the study of new monomers. However, the chemistry of the polymerization of thiophene and its derivatives has received little attention. Moreover, none of the previous methods for the synthesis of electrically conducting polythiophene and its derivatives involves using organic initiators as in the present invention.
Accordingly, higher yielding and more effective cost and energy efficient methods of producing polythiophene and its derivatives are needed.